Effect of non-linear flow behavior on heat transfer in a thermoacoustic engine core

The non-linear behavior of the temperature field in a thermoacoustic engine core is explored using computational fluid dynamics (CFD) simulations; the effect of that behavior on heat transfer is estimated. With respect to heat transfer in a thermoacoustic core (TAC), the unsteady behavior of this temperature field and its influence has not been discussed sufficiently so far. In the present study, to understand this non-linear behavior in oscillatory flows, both CFD simulation and numerical heat transfer analysis, which is combined with standard thermoacoustic linear theory, are performed. The simulated environment is a standing-wave acoustic field in a straight-channel thermoacoustic device. With a comparison of the CFD and heat transfer analyses, differences in the temperature field behavior are discussed. Whereas the acoustic field is sinusoidal in the TAC for both calculations, only the CFD result shows non-linear behavior in the unsteady temperature field. This arises from the interaction between the fluid motion and the fluid temperature, which varies spatially in the streamwise direction. This feature reflects the heat flux on the walls of the heat exchanger. Ultimately, this effect causes around 10% of the difference in estimating the heat transfer in the TAC.